Update the Consul and Vault configs to take advantage of their
included `go-sockaddr` library for getting the IP addresses we need in
a portable way. This particularly avoids problems with "predictable"
interface names provided by systemd.
Also adds the `sockaddr` binary to the Packer build so we can use it
in our provisioning scripts.
Make a clear split between Packer and Terraform provisioning steps:
the scripts in the `packer/linux` directory are run when we build the
AMI whereas the stuff in shared are run at Terraform provisioning time.
Merging all runtime provisioning scripts into a single script for each
of server/client solves the following:
* Userdata scripts can't take arguments, they can only be templated
and that means we have to do TF escaping in bash/powershell scripts.
* TF provisioning scripts race with userdata scripts.
